Surface-emitting laser diode array and driving method thereof, photodetector, photodetector array, optical interconnection system, and multiwavelength optical communication system

Abstract

A surface-emitting LD array includes a plurality of surface-emitting LDs respectively including secondary diffraction gratings produced at the same pitch. These LDs are radially arranged on the substrate with a prescribed point on the substrate as the center of the radial arrangement so that the secondary diffraction gratings face to the center point. In this structure, the laser oscillation regions of the adjacent surface-emitting LDs are spaced apart from each other, so that the respective surface-emitting LDs are operated individually with high stability. As the result, when these surface-emitting LDs are oscillated with the same driving current, a high power laser light comprising a plurality of laser lights that are emitted from the respective LDs and have the same phase and the same wavelength is output stably in a prescribed direction. On the other hand, when these surface-emitting LDs are oscillated with different driving currents, a phase composite wave in which a plurality of laser lights having the same phase and different wavelengths are compounded is output stably in a prescribed direction.

What is claimed is: 
     
       1. A surface-emitting laser diode array including: a substrate having a center point; and   a plurality of surface-emitting laser diodes respectively including secondary diffraction gratings having identical pitches and radially arranged on the substrate so that the secondary diffraction gratings face the center point of the substrate wherein the surface-emitting laser diodes are driven with different driving currents and to output respective laser light beams perpendicular to the substrate and having identical wavelengths and different phases that combine as a phase composite light beam steerable in three dimensions about the center point.   
     
     
       2. The surface-emitting laser diode array of claim 1 wherein said secondary diffraction gratings respectively include, periodically arranged along straight line segments, projections that are perpendicular to radii extending from the center point of the substrate. 
     
     
       3. The surface-emitting laser diode array of claim 1 wherein the substrate is a semiconductor substrate and the surface-emitting laser diodes are simultaneously produced on the semiconductor substrate. 
     
     
       4. The surface-emitting laser diode array of claim 2 wherein the substrate is a semiconductor substrate and the surface-emitting laser diodes are simultaneously produced on the semiconductor substrate. 
     
     
       5. The surface-emitting laser diode array of claim 3 including a plurality of grooves for heat radiation disposed in the substrate between adjacent surface-emitting laser diodes. 
     
     
       6. The surface-emitting laser diode array of claim 4 including a plurality of grooves for heat radiation disposed in the substrate between adjacent surface-emitting laser diodes. 
     
     
       7. The surface-emitting laser diode array of claim 1 wherein the substrate is an insulating substrate and the surface-emitting laser diodes are fabricated individually and mounted on the insulating substrate. 
     
     
       8. The surface-emitting laser diode array of claim 2 wherein the substrate is an insulating substrate and the surface-emitting laser diodes are fabricated individually and mounted on the insulating substrate. 
     
     
       9. The surface-emitting laser diode of claim 1 wherein driving currents applied to the respective surface-emitting laser diodes are controlled to change output direction of a composite laser light comprising laser light beam emitted from the respective laser diodes in an arbitrary direction. 
     
     
       10. The surface-emitting laser diode of claim 2 wherein driving currents applied to the respective surface-emitting laser diodes are controlled to change output direction of a composite laser light comprising laser light beam emitted from the respective laser diodes in an arbitrary direction. 
     
     
       11. A surface-emitting laser diode array including: a substrate having a main surface and a through-hole perpendicular to the main surface;   a plurality of laser diodes, each laser diode including a facet from which laser light is emitted in a direction parallel to the main surface of the substrate, and radially arranged on the main surface of the substrate with the laser emitting facets of the respective laser diodes facing the through-hole in the substrate; and   means for collecting laser light emitted from the respective laser diodes and outputting the collected laser light in a direction perpendicular to the main surface of the substrate.   
     
     
       12. The surface-emitting laser diode array of claim 11 wherein said laser diodes are distributed feedback laser diodes or distributed Bragg reflector laser diodes including primary diffraction gratings. 
     
     
       13. The surface-emitting laser diode array of claim 12 wherein the primary diffraction gratings of the respective laser diodes have identical pitches and oscillate at identical oscillation wavelengths. 
     
     
       14. The surface-emitting laser diode array of claim 12 wherein the primary diffraction gratings of the respective laser diodes have different pitches and oscillate at different wavelengths. 
     
     
       15. The surface-emitting laser diode array of claim 12 wherein the laser diodes are arranged so that projections of the primary diffraction gratings of adjacent laser diodes are not centric with the through-hole of the substrate. 
     
     
       16. The surface-emitting laser diode array of claim 14 wherein the laser diodes are arranged so that projections of the primary diffraction gratings of adjacent laser diodes are not centric with the through-hole of the substrate. 
     
     
       17. The surface-emitting laser diode array of claim 11 wherein the substrate is a semiconductor substrate and the laser diodes are simultaneously produced on the semiconductor substrate. 
     
     
       18. The surface-emitting laser diode array of claim 17 including a plurality of grooves for heat radiation disposed in the substrate between adjacent laser diodes. 
     
     
       19. The surface-emitting laser diode array of claim 11 wherein the substrate is an insulating substrate and the laser diodes are fabricated individually and mounted on the insulating substrate. 
     
     
       20. A spatial optical interconnection system comprising: a semiconductor light emitting element for converting electrical signals into optical signals and for radiating the optical signals into space, the semiconductor light emitting element comprising a substrate and a plurality of surface-emitting laser diodes respectively having secondary diffraction gratings having the same pitch and radially arranged on the substrate so that the secondary diffraction gratings face a point on the substrate, wherein the laser diodes are driven with different driving currents to output respective laser light beams perpendicular to the substrate and having identical wavelengths and different phases that combine as a phase composite light beam steerable in three dimensions about the point; and   a photodetector for receiving the phase composite light beam and converting the phase composite light beam to an electrical signal.   
     
     
       21. The spatial optical interconnection system of claim 20 wherein the driving currents of the respective laser diodes are controlled to steer the phase composite light beam.